1. Field of the Invention
This invention relates to CDMA systems, and more specifically to cell identification using inter-frequency measurements in CDMA systems.
2. Description of the Related Art
In Code Division Multiple Access (CDMA) systems, a soft handover (SHO) area is characterized by similarly strong pilot power signals (CPICH Ec/Io in Wideband CDMA (WCDMA)). Pilot powers are measured by the mobile device in idle as well as in connected mode. In connected mode, it is very important that the mobile device (UE) is always connected to the optimum cell(s). Otherwise, it would cause significant interference in an uplink and waste network capacity. In idle mode, it is important to camp in the strongest cell to allow a quick call initiation and not cause interference during call initiation.
The uplink interference to the neighboring cells in WCDMA may be avoided with (1) soft handover within one frequency based on downlink CPICH Ec/Io measurements, or (2) “downlink dying first” with adjacent channel interference. These methods work when there is a fixed pair of uplink and downlink as in the Universal Mobile Telecommunications System (UMTS) core band in 2.1 GHz. This approach cannot be applied for 2.5 GHz when the same uplink carrier in 1.9 GHz can be paired with downlink in 2.1 GHz or in 2.5 GHz. Therefore, new approaches are needed to avoid the uplink interference.